The present invention relates to body implantable connecting devices for extending cardiac pacing leads, defibrillation leads and the like, and more particularly to means for sealing electrically conductive connectors in such devices.
Certain particularly useful medical treatment systems involve body implantable devices that deliver pulses of electrical energy to stimulate body tissue. Perhaps the best known of these devices is the cardiac pacer, which includes a pulse generator having a power source and electrical circuitry for generating timed electrical pulses. The pulses are delivered through an electrically conductive lead having proximal end terminals connected to the pulse generator, and one or more distal end electrodes secured to myocardial tissue (for example) at a location remote from the pulse generator.
A more recent stimulating device is the defibrillator, designed to terminate arrhythmias such as ventricular fibrillation or tachycardia, by application of one or more properly timed electrical pulses to the heart. The defibrillator differs from the pacer in that the electrical pulses involved are of greater intensity, and delivered only in response to sensing arrhythmias. Other devices, e.g. neuromuscular stimulators, involve implantable means: for delivering electrical impulses to stimulate tissue.
In all of these devices, there is a need for electrically and mechanically coupling the proximal ends of leads to the remainder of the tissue stimulating system, in a manner which is convenient, yet preserves mechanical integrity and provides a highly conductive path for electrical pulses and electrically isolates the conductive path from surrounding bodily tissue. Further, given the limited time and other constraints of implant procedures, it is desirable to provide connection means conveniently accessible to alternatively connect and disconnect the proximal end lead terminals. The connection can occur at a pulse generator, or at an adapter used between electrical leads of different sizes or types, or simply to extend the length of the conductive path.
An example of such connection in a pacer is disclosed in U.S. Pat. No. 3,822,707 (Adducci et al), in which proximal segments 19 and 20 of a lead are received respectively in sleeves 24 and 25 in the pulse generator. The segments are retained by Allen head set screws, with insulating rubber plugs inserted after the screws to electrically isolate them from the body cavity environment. In U.S. Pat. No. 3,908,668 (Bolduc) terminal pins of a lead are inserted into receptacles provided in a pulse generator, and retained by set screws 42. A rubber grommet 54 is placed over the set screws and is pierced through at a pair of protrusions, to admit a tool for turning the set screws. The grommet self seals when the tool is withdrawn.
Other means for connecting leads to body implantable devices are shown in U.S. Pat. No. 4,461,194 (Moore) in which a seal plug 36 is positioned between a set screw 32 and a cap 42, U.S. Pat. No. 4,583,543 (Peers-Trevarton) featuring an Allen screw with a pointed tip for forcing a side wall of a metal tube into contact with a lead terminal pin, and U.S. Pat. No. 4,784,141 (Peers-Trevarton) directed to a lead locking mechanism having a hollow screw coaxial with the lead being connected. In U.S. Pat. No. 4,774,953 (Foote), one end of a grub screw 32 protrudes into a lead retaining opening to secure the lead.
Plug seals having self-sealing passages have been found particularly advantageous in connection with cardiac pacers, as they afford quick and convenient tool access for securing lead terminal ends within a pulse generator, and for releasing such terminal ends. The capability of the plug to re-seal itself upon withdrawal of the tool, however, depends upon the dimensional integrity of the housing in which the plug is mounted. Pulse generators typically are constructed of rigid material well suited for this purpose, in that the diameter of openings containing the plugs is controlled. Adapters and lead extenders, however, frequently are constructed of silicone rubber or other resilient elastomeric material. Consequently the openings formed in such adapters for retaining plug seals do not provide the necessary rigidity, leading to alternative means for protecting the electrically conductive connectors housed in flexible adapters and the like.
For example, once the set screws have been adjusted to properly connect the lead, an uncured silicone rubber adhesive can be applied over the heads of the screws, to begin curing before the surgical site is closed. This adhesive, however, gives off acetic acid as it cures and can irritate the incision area. Once in place, this type of seal allows no further tool access. Another approach is to provide a flap seal which covers one or more opening containing set screws, and is sufficiently thin to be folded or rolled over upon itself to expose the openings and admit a tool to adjust the set screws. Flap seals are difficult to construct, however, and have a tendency to bond to themselves, which can result in a tearing of the flap as the physician attempts to move it into sealing position over the set screw openings.
Therefore, it is an object of the present invention to provide a reliable means for sealing terminal connection set screws in a flexible or resilient adapter, to electrically isolate the set screws and protect them from exposure to bodily fluids around the adapter.
Another object of the invention is to provide a means for sealing electrically conductive adjustable contacts, mounted within flexible housings, from the exterior of the housings and provide convenient access to adjust the contacts without removing the sealing means.
Yet another object of the invention is to provide a means for adapting selected plug mounting regions of a resilient adapter, such that the selected regions provide a controlled, rigid support of tool admitting and self-sealing plugs.